1. Field of the Invention
This invention relates to a computer-assisted reflectance-based object detection system and, more specifically, to a detection system having a display device as a light source.
2. Background
Reflectance-based object detection devices are currently known. The reflectance channel from a laser rangefinder is used to detect small obstacles on a highway. Photometric stereo recovers depth information by illuminating a scene from a variety of controlled directions.
Computer monitors, in addition to being display devices, can also serve as illumination sources, for example, for computer vision applications. However, the main limitation to using a monitor as a programmable illumination source is that monitor brightness is typically low compared with ambient illumination. Thus, differences in the brightness of the surroundings due to changes in the monitor""s illumination can be small. The precision with which depth information can be recovered, therefore, is restricted.
It is an object of the present invention to provide a method and apparatus for analyzing the differences in the brightness of a computer""s surroundings using a display device as a light source.
Accordingly, we have developed a method and apparatus to accurately detect the differences in scene brightness due to changes in a display device""s illumination by accumulating information from a sequence of images.
A display device may be any display device, for example, a computer monitor, a CRT display, or a backlit LCD display. Thus, throughout the specification and the claims, the words display device and monitor are used interchangeably.
The present invention includes a computer having a processor. A display device is connected to the computer. The processor causes at least two different patterns to be displayed successively on the display device. A camera is connected to the computer and is directed towards objects in front of the display device. The processor controls the camera such that each time a pattern is displayed on the display device at least one image of the surroundings is captured. The captured images are aligned and differ substantially only in scene illumination. The processor combines the captured images to create a difference image. The difference image is analyzed to interpret the objects in the surroundings. For example, calculations may be performed to segment the foreground from the background of the surroundings or to estimate the range (distance) of at least one object from the display device.